Stop vendoring resx for vendored microsoft code (#8461)

## Summary of changes

Stop vendoring the `SR` + regex files for microsoft code

## Reason for change

Using `ResourceManager` is overkill, as we don't deploy all the
translations etc anyway, and don't want to.

## Implementation details

Replaced all the `SR.` accesses in previous PRs, so this is now dead
code that we can remove.

## Test coverage

If it builds, we're good

## Other details

https://datadoghq.atlassian.net/browse/APMLP-1207

Note that currently, there's a lot of `Utf8Formatter` code that _isn't_
used, and could be excluded, however, given that theoretically we
could/should use this in the future. I'm torn whether to just leave it
in, or whether to tear it out for now, and restore it if/when we want to
use it later. Any thoughts?

Part of a stack updating our vendored system code

- #8391
- #8454
- #8455
- #8459

Author: andrewlock

tracer/build/_build/UpdateVendors/VendoredDependency.cs

@@ -230,19 +230,6 @@ static VendoredDependency()
                 },
                 relativePathsToExclude: new [] { "Resources/Strings.resx" });
 
-            Add(
-                libraryName: "System.Private.CoreLib",
-                version: "1.0.0",
-                downloadUrl: "https://github.com/DataDog/dotnet-vendored-code/archive/refs/tags/1.0.0.zip",
-                pathToSrc: new[] { "dotnet-vendored-code-1.0.0", "System.Reflection.Metadata", "System.Private.CoreLib" },
-                transform: filePath =>
-                {
-                    
-                    RewriteCsFileWithStandardTransform(filePath, originalNamespace: "System.Runtime", AddNullableDirectiveTransform, AddIgnoreNullabilityWarningDisablePragma);
-                    RewriteCsFileWithStandardTransform(filePath, originalNamespace: "System.Diagnostics", AddNullableDirectiveTransform, AddIgnoreNullabilityWarningDisablePragma);
-                    RewriteCsFileWithStandardTransform(filePath, originalNamespace: "FxResources", AddNullableDirectiveTransform, AddIgnoreNullabilityWarningDisablePragma);
-                });
-
             // "Common" shared components required by System.Reflection.Metadata (among others)
             // Not a "real" package
             Add(